Typically, the borehole wall of an oil or gas well is lined with a heavy-weight steel pipe that is secured in place by cement. The cement is injected into the annulus between the pipe O.D. and the raw-cut wall of the bore-hole. The first string of such cement-set pipe extending down from the surface or rig floor is generally characterized as surface casing. For many reasons, such as an extremely deep well, one or more smaller diameter casings may be suspended from the bottom end of the surface casing. Often, the smaller, internal casing is characterized as a casing liner or simply, a liner.
The mechanism for suspending a liner from within the substantially smooth, internal bore wall of an up-hole support casing, for example, is a plurality of pipe slips around the perimeter of the liner pipe near the liner pipe upper end. These slips have rows of hardened teeth, points or edges that penetrate the inside wall of the support casing as the teeth are forced radially out from the liner by cooperative wedge faces. Once set, the slip teeth (wickers) penetrate the support casing wall as a function of the suspended weight. When extremely long and/or heavy liners are suspended, attention is given to the capacity of the upper support casing for supporting the weight suspended from it.
The liner hanger usually includes means for pressure sealing the hanger joint whereby the interior bore of the casing/liner is hydrodynamically isolated from the casing/liner exterior. Testing the integrity of the hanger seal is a brief but important step in the well completion sequence.
Traditionally, the integrity of a liner hanger is tested by plugging the liner mouth with an elastomer plug seal (packer) around the annulus between the workstring tubing and the internal bore wall of the liner. Subsequently, the upper well annulus is pressurized to monitor the reverse flow response to the hydrostatic pressure head within the workstring bore. The risks attendant with this traditional procedure, however, include, first, the loading forces on the elastomer plug to seal it in the liner bore. These forces are entirely carried by the liner hanger. Secondly, the hydraulic test pressure differentials are carried by the liner sectional area. These pressure differentials may be considerable and are also carried directly by the liner hanger. Accordingly, when added to the load of a heavy liner, loads imposed as an incident of testing a liner hanger may exceed the support capacity of the hanger and/or the support casing.
It is, therefore, an object of the present invention to provide the art with a tool and procedure for limiting the pressure load on a liner hanger when testing the integrity of the hanger pressure seal.
Also an object of the invention is a liner top test packer that seals the annulus between the workstring and the casing that supports the liner hanger.
Another object of the invention is a liner top test packer that is set against the support casing bore in conjunction with workstring anchor slips.